The present invention relates to a data readable an d writable optical disk and an optical disk apparatus for driving it.
In a rewritable optical disk capable of repeatedly writing data in arbitrary positions on the disk and reading out data from arbitrary positions on the disk, data is generally written in units of one sector. In each sector, sector address data and error correction coded data are written.
To the contrary, in a recently standardized large-capacity rewritable optical disk 120 mm in diameter called a DVD-RAM, data can be written in units of not one sector but one error correction block (ECC block) obtained by error correction coding of a plurality of sectors in order to improve the data error correction ability. Similarly, in a DVD-ROM as a read-only optical disk, data is written in units of one error correction block formed from 16 sectors each including 2,048-byte data. In the DVD-ROM, both an error correction block and sector address information undergo error correction coding similar to data, thereby attaining a structure virtually free from any error.
In the DVD-RAM, address information in unit of one sector are written as emboss pits in the disk in advance. In writing data, a plurality of sectors (16 sectors) constitute one error correction block. Thus, address information can always be obtained in units of one sector. Even when, for example, the optical head erroneously moves to an adjacent track during writing, the write error can be limited to one sector, and the seek time can be shortened. Further, since a periodic signal corresponding to the sector period can always be obtained from the address information of a sector during a write/read, the spindle motor for rotating the optical disk can be controlled in accordance with this periodic signal.
In a method of writing address information in units of one sector, like a conventional DVD-RAM, each sector must have many areas other than the area for writing data, such as a buffer area for coping with a change in actual sector length on the disk caused by variations in rotation speed or decentering of the disk during writing/reading out data, and a buffer area for co ping with random shifts of write-in positions and deterioration of start and end positions in the phase change recording scheme, in addition to the address information area (header field). This decreases the format efficiency. To ensure a sufficient write-in capacity, the write-in density must be increased. If the write-in density is not changed, the write-in density decreases.
As a method of writing data in an optical disk without forming address information in units of one sector, a groove in the optical disk is wobbled to write address information as an FM signal, and data is written in units of one error correction block on the basis of the address information. This is employed in a CD-R, CD-RW, and the like. In this case, the address of an error correction block is determined only after data is written, so data is generally difficult to efficiently write in an arbitrary position.
The address information of an error correction block and the address information of a sector cannot be extracted unless error correction coded data is decoded. If an address error occurs during a write, the error cannot be corrected, and data may be written in an erroneous address. Furthermore, the error correction must be executed for the address information even if the seek operation is performed for another track. As a result, the time required for seeking a target address becomes long, so that the wait time in data reading and writing becomes long. In addition, address information written as a groove wobble may deteriorate during a several number of writes.
In an area where data is written, a periodic signal corresponding to the sector period necessary to control the spindle motor can be obtained from the optical disk. However, in an area where no data is written, no periodic signal can be obtained. Finalization for writing a dummy signal for generating a periodic signal must be performed for a plurality of tracks after data is written, which prolongs the write-in time.
As described above, of conventional rewritable optical disks, an optical disk for writing address information in units of one sector as pre-pits requires, for each sector, buffer areas for coping with a change in actual sector length resulting from variations in rotation speed or decentering of the disk and coping with random shifts of write-in positions and deterioration of start and end positions in the phase change recording scheme. This increases the number of areas other than the area for writing data and decreases the format efficiency.
In an optical disk in which a groove is wobbled to write address information and data is written in units of one error correction block, data is difficult to efficiently write in an arbitrary position. Address information in units of one sector cannot be obtained unless error correction coded data is decoded. Moreover, finalization for generating a periodic signal for controlling the spindle motor must be performed to extend the write-in time.